1. Field of the Invention
The present invention relates to a yellow toner for flash fixation used in forming an image in an electrophotographic system, and a developer and an image forming method using the same.
2. Description of the Related Art
In recent years, demand for mass printing has been increasing to print materials such as newspapers and direct mails by electrophotography using electrophotographic toners in the field of high-speed printing. It is known that image printing by electrophotography using flash fixation methods makes far higher printing speeds possible as compared with electrophotographic image printing using thermal fixation methods associated with the use of a heat roll or the like (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 60-63545, 60-63546, 60-57858, 60-57857, 58-102248, 58-102247, 60-131544, 60-133460, 61-132959, 2000-147824, 7-191492, 2000-155439, 6-348056, 10-39535, 2000-35689, 11-38666, 11-125930, 11-125928, 11-125929, and 11-65167). This is due to the fact that with flash methods, there is less contact between the members and the recording media. In flash fixation methods, however, when radiating light onto color toner, the efficiency of converting the light to heat is lower than when radiating light onto monochrome toner. It is therefore impossible to use color toners that are used in thermal fixation methods, as they are, in flash fixation methods. Thus, in flash fixation methods, it is known to use toners to which infrared absorbents that have low visible ray wavelength absorption are added.
Examples of compounds known as the infrared absorbents added to such toners include onium compounds (such as aminium derivatives and diimmonium derivatives), cyanine compounds, nickel complex compounds, phthalocyanine compounds, and ytterbium oxide compounds. Usually, the infrared absorbent is added to the inside of the toner, however, a technique of adhering the infrared absorbent to the outside of the toner is also known (see JP-A No. 2002-156779).
In the case of color toners for thermal fixation methods using no infrared absorbent, for example, benzimidazolone (C. I. Pigment Yellow 180 or the like), naphthol carmine F6B (C. I. Pigment Red 184 or the like) and β copper phthalocyanine (C. I. Pigment Blue 15:3 or the like) are respectively used as pigments for yellow toners, pigments for magenta toners and pigments for cyan toners (see JP-A No. 2000-199982).
Isoindoline compounds (C. I. Pigment Yellow 185 or the like), monoazo litolrubin and β copper phthalocyanine (C. I. Pigment Blue 15:3 or the like) are also respectively used as pigments for yellow toners, pigments for magenta toners and pigments for cyan toners (see JP-A No. 9-166889).
However, all infrared absorbents have color since infrared absorbents slightly absorb light having visible ray wavelengths. Therefore, when a toner to which an infrared absorbent is added is used to form a full color image with a flash fixation method, problems occur. Specifically, when the same pigment as used in thermal fixation toners is used as a colorant added to the above-mentioned toner, all of the color is shifted by the effect of the color of the added infrared absorbent. Even if the toner having shifted color(s) is used and the color of the formed image is adjusted by means of an image forming device, sufficient color reproducibility cannot be obtained. Therefore, for example, in yellow toners to which an infrared absorbent colored into green, such as a naphthalocyanine compound or an onium compound, is added, the color thereof is shifted toward a green color.
Therefore, in order to obtain a yellow toner for flash fixation excellent in color reproducibility for full color or business color usage, it is necessary to correct color shift resulting from the added infrared absorbent.
Accordingly, there is a need for a yellow toner for flash fixation wherein color shift resulting from an infrared absorbent is corrected to exhibit superior color reproducibility, and an electrographic developer and an image forming method using the yellow toner.